Gold plating processes have many industrial applications including production of jewelry and other decorative articles, production of optical devices and production of electronic circuits and components. There are several advantages to the use of gold. First of all, it does not form a surface insulating film such as an oxide film. For this reason, gold has a high surface luster which is quite attractive when used in jewelry articles. For the same reason, the optical reflection properties of gold are attractive, which makes its use in optical devices highly desirable. Again, for the same reason, its use in electric circuits and components is highly desirable because surface contact to gold usually has low electrical resistance.
Gold also has the advantage of being chemically inert. This is due to the fact that no surface insulating layer is formed on gold. The use of gold often increases the lifetime and reliability of devices and articles since gold is not affected by many chemicals and adverse conditions of temperature and humidity. A particular case in point is the production of integrated electronic circuits. Here quite thin and narrow conducting paths are required. Many metals (i.e., copper) might be satisfactory as far as electrical conductivity is concerned, but they rapidly degrade with time. Gold has the advantage of being inert, and also has quite high electrical conductivity.
Because of its excellent electrical contact properties, gold is often used in electrical connectors, switches and relays. By the addition of small amounts of various elements (for example, arsenic, cobalt, nickel), gold can be made quite hard and resistant to abrasion. For the above reasons, and because of the extensive growth of the integrated circuit industry, the industrial use of gold has increased tremendously in recent years. This fact, together with the high and increasing cost of gold has made it highly desirable to use gold in as efficient a manner as possible. In particular, it has become economically desirable to ensure that gold not actually plating onto a surface is recovered and not lost.
In many processes involving gold, such as gold plating processes, extensive use is made of rinse water to remove various reagents and prevent contamination of solutions used in subsequent steps in the process. Such rinsing operations are useful in all types of processes involving gold including, electroplating, electroless plating (displacement and autocatalytic plating), etc. Where gold plating solution is removed by the rinse water, significant amounts of gold are lost which adds to the cost of the plating process. It is highly desirable from an economic point of view to recover this gold. Also, from an ecological point of view, removal of gold from rinse water is desirable.